/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.andengine.util.base64;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * An InputStream that does Base64 decoding on the data read through
 * it.
 */
public class Base64InputStream extends FilterInputStream {
    private final Base64.Coder coder;

    private static byte[] EMPTY = new byte[0];

    private static final int BUFFER_SIZE = 2048;
    private boolean eof;
    private byte[] inputBuffer;
    private int outputStart;
    private int outputEnd;

    /**
     * An InputStream that performs Base64 decoding on the data read
     * from the wrapped stream.
     *
     * @param in    the InputStream to read the source data from
     * @param flags bit flags for controlling the decoder; see the
     *              constants in {@link Base64}
     */
    public Base64InputStream(final InputStream in, final int flags) {
        this(in, flags, false);
    }

    /**
     * Performs Base64 encoding or decoding on the data read from the
     * wrapped InputStream.
     *
     * @param in     the InputStream to read the source data from
     * @param flags  bit flags for controlling the decoder; see the
     *               constants in {@link Base64}
     * @param encode true to encode, false to decode
     * @hide
     */
    public Base64InputStream(final InputStream in, final int flags, final boolean encode) {
        super(in);
        this.eof = false;
        this.inputBuffer = new byte[BUFFER_SIZE];
        if (encode) {
            this.coder = new Base64.Encoder(flags, null);
        } else {
            this.coder = new Base64.Decoder(flags, null);
        }
        this.coder.output = new byte[this.coder.maxOutputSize(BUFFER_SIZE)];
        this.outputStart = 0;
        this.outputEnd = 0;
    }

    @Override
    public boolean markSupported() {
        return false;
    }

    @Override
    public void mark(final int readlimit) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void reset() {
        throw new UnsupportedOperationException();
    }

    @Override
    public void close() throws IOException {
        this.in.close();
        this.inputBuffer = null;
    }

    @Override
    public int available() {
        return this.outputEnd - this.outputStart;
    }

    @Override
    public long skip(final long n) throws IOException {
        if (this.outputStart >= this.outputEnd) {
            this.refill();
        }
        if (this.outputStart >= this.outputEnd) {
            return 0;
        }
        final long bytes = Math.min(n, this.outputEnd - this.outputStart);
        this.outputStart += bytes;
        return bytes;
    }

    @Override
    public int read() throws IOException {
        if (this.outputStart >= this.outputEnd) {
            this.refill();
        }
        if (this.outputStart >= this.outputEnd) {
            return -1;
        } else {
            return this.coder.output[this.outputStart++];
        }
    }

    @Override
    public int read(final byte[] b, final int off, final int len) throws IOException {
        if (this.outputStart >= this.outputEnd) {
            this.refill();
        }
        if (this.outputStart >= this.outputEnd) {
            return -1;
        }
        final int bytes = Math.min(len, this.outputEnd - this.outputStart);
        System.arraycopy(this.coder.output, this.outputStart, b, off, bytes);
        this.outputStart += bytes;
        return bytes;
    }

    /**
     * Read data from the input stream into inputBuffer, then
     * decode/encode it into the empty coder.output, and reset the
     * outputStart and outputEnd pointers.
     */
    private void refill() throws IOException {
        if (this.eof) {
            return;
        }
        final int bytesRead = this.in.read(this.inputBuffer);
        boolean success;
        if (bytesRead == -1) {
            this.eof = true;
            success = this.coder.process(EMPTY, 0, 0, true);
        } else {
            success = this.coder.process(this.inputBuffer, 0, bytesRead, false);
        }
        if (!success) {
            throw new IOException("bad base-64");
        }
        this.outputEnd = this.coder.op;
        this.outputStart = 0;
    }
}
